Compared to men, women are both at increased risk of smoking-related morbidity and mortality, and have increased difficulty achieving smoking abstinence. Sex hormones (specifically progesterone, allopregnanolone, and estradiol) have been implicated in both the animal and clinical literature as having an effect on addictive behaviors. These sex hormones increase dramatically during pregnancy, providing an ideal clinical model for further investigation into this association. Therefore, the objective of this project is to investigate the relationship between sex hormones and smoking-related symptomatology in pregnancy and, a more controlled clinical model, oral contraceptives. We will address this objective by assessing two specific study aims: (1) investigate the association between levels of progesterone (Prog), allopregnanolone (Allo) and the estradiol/progesterone (E2/P) ratio with smoking-related symptomatology during ad libitum smoking, and (2) examine the association between levels of Prog, Allo and E2/P with the changes in smoking-related symptomatology and response to nicotine following overnight smoking abstinence. These aims will be investigated by conducting one study with two samples: Sample 1 will be pregnant women (n=84) at either 16- 20 or 32-36 weeks gestation (two time points selected to ensure large variability in sex hormone levels). Sample 2 will incorporate a cross-over design to investigate low versus high levels of progesterone in a sample of oral contraceptive (OC) users (n=52). Participants in both samples will complete identical data collection procedures including providing biological samples of saliva (cortisol for stress), urine (nicotine exposure) and blood (sex hormones), as well as six days of ecological momentary assessments. Participants will also complete a nicotine response lab session following overnight abstinence. This study has several innovative aspects. Specifically, we will be among the first to investigate the association between sex hormones and smoking-related symptomatology during pregnancy, characterize allopregnanolone in pregnancy, and compare the effects of sex hormones on smoking-related symptomatology within two clinical models (pregnancy and OC users) known to have different levels of sex hormones. If our hypotheses are confirmed, the results of this study will advance the literature on the role of sex hormones in addictive behaviors. Further, this study has the potential to inform new and innovative smoking cessation treatments for women of childbearing age.